A device commonly referred to as a power bank includes a rechargeable battery, buck converter circuitry, boost converter circuitry, an input connector, and an output connector. In one conventional power bank, the rechargeable battery has an operating range from about 2.8 volts for a fully discharged battery to about 4.35 volts for a fully charged battery. If the battery is undesirably discharged, then an external DC power source can be plugged into the input connector of the power bank. The external DC power source supplies a DC voltage, such as 5.0 volts DC, onto the input connector of the power bank. Buck converter circuitry within the power bank receives the 5.0 volt power from the input conductor and bucks the voltage down and supplies a constant charging current to the battery at the lower battery voltage. As the battery charges, the battery voltage increases up to its fully charged battery voltage of 4.35 volts. Provided that the battery voltage is higher than the 2.8 volt fully uncharged battery value, the power bank is usable to supply a 5.0 volt output voltage to an external load device. To power the external load device, the external load device is plugged into the output connector. The boost converter circuitry within the power bank receives power from the rechargeable battery at the lower battery voltage, boosts the voltage up, and supplies a higher voltage regulated 5.0 volts out of the output connector and to the load device.